There is known a conventional control device that includes: a controller that outputs a control signal for controlling the drive of a load; and a driving circuit that supplies a driving current from a power source to the load to drive the load on the basis of the control signal from the controller.
When an abnormal large current flows into its inside from any cause, the driving circuit may enter an overheated state to be destroyed. For this reason, there is a control device that includes: a temperature detecting unit that detects a temperature near the driving circuit; and a controller that monitors the temperature detected by the temperature detecting unit and blocks the supply of a driving current to the load when it is determined that the driving circuit enters an overheated state (for example, see Japanese Laid-open Patent Publication No. 2009-284576).
In addition to the configuration that the controller determines an overheated state, there is a control device that has a configuration that the driving circuit itself determines an overheated state and blocks the supply of a driving current to a load so as to beforehand prevent the burnout destruction of the driving circuit more surely.
The driving circuit of the control device includes a temperature detecting unit that outputs the detected temperature to an overheat determining unit in the driving circuit, separately from the temperature detecting unit that outputs the detected temperature to the controller. When the overheat determining unit determines that the temperature is not less than a temperature threshold, the driving circuit blocks the supply of a driving current to the load.
As a result, when the control device cannot prevent the burnout destruction of the driving circuit by requiring time in an overheated state determination process performed by the controller due to the instant rising of the temperature of the driving circuit, the driving circuit can immediately block the supply of a driving current to the load.
However, the temperature detecting unit in the driving circuit may break down. In this case, because the controller cannot determine the presence or absence of a failure of the temperature detecting unit in the driving circuit, the control device cannot prevent the burnout destruction of the driving circuit in that an overheated state determination process performed by the controller causes delay when the temperature of the driving circuit instantly rises as described above.